From b13f7b9e148cd19b2021c306fd97769cff69ab45 Mon Sep 17 00:00:00 2001
From: Lukasz Mierzwa <lukasz@cloudflare.com>
Date: Fri, 17 Nov 2023 11:01:09 +0000
Subject: [PATCH] Fix false positive reports from promq/regexp

Fixes #782.
---
 docs/changelog.md                     | 6 ++++++
 internal/checks/promql_regexp.go      | 8 ++++++++
 internal/checks/promql_regexp_test.go | 7 +++++++
 3 files changed, 21 insertions(+)

diff --git a/docs/changelog.md b/docs/changelog.md
index ec9e99ce..02b11d33 100644
--- a/docs/changelog.md
+++ b/docs/changelog.md
@@ -1,5 +1,11 @@
 # Changelog
 
+## v0.49.2
+
+### Fixed
+
+- Fixed false positive reports from `promql/regexp` - #782.
+
 ## v0.49.1
 
 ### Fixed
diff --git a/internal/checks/promql_regexp.go b/internal/checks/promql_regexp.go
index 5b0485d0..85fae50a 100644
--- a/internal/checks/promql_regexp.go
+++ b/internal/checks/promql_regexp.go
@@ -53,7 +53,15 @@ func (c RegexpCheck) Check(_ context.Context, _ string, rule parser.Rule, _ []di
 			var isUseful bool
 			var beginText, endText int
 			r, _ := syntax.Parse(re, syntax.Perl)
+			if r.Flags > 0 && r.Flags != syntax.Perl {
+				// If effective flags are different from default flags then we assume regexp is useful.
+				// It could be case sensitive match.
+				isUseful = true
+			}
 			for _, s := range r.Sub {
+				if s.Flags > 0 && s.Flags != syntax.Perl {
+					isUseful = true
+				}
 				// nolint: exhaustive
 				switch s.Op {
 				case syntax.OpBeginText:
diff --git a/internal/checks/promql_regexp_test.go b/internal/checks/promql_regexp_test.go
index 59da655f..2c5afd13 100644
--- a/internal/checks/promql_regexp_test.go
+++ b/internal/checks/promql_regexp_test.go
@@ -174,6 +174,13 @@ func TestRegexpCheck(t *testing.T) {
 				}
 			},
 		},
+		{
+			description: "regexp with a modifier",
+			content:     "- record: foo\n  expr: foo{job=~\"(?i)someone\"}\n",
+			checker:     newRegexpCheck,
+			prometheus:  noProm,
+			problems:    noProblems,
+		},
 	}
 	runTests(t, testCases)
 }